Thermosetting resin composition and method of producing the same

ABSTRACT

A thermosetting resin composition including: a matrix including a thermosetting resin and an elastomer; and carbon nanofibers dispersed in the matrix. The elastomer includes an unsaturated bond or a group having affinity to the carbon nanofibers.

Japanese Patent Application No. 2005-327404, filed on Nov. 11, 2005, andJapanese Patent Application No. 2006-82871, filed on Mar. 24, 2006, arehereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a thermosetting resin composition and amethod of producing the same.

A composite material has been generally provided with physicalproperties corresponding to the application by combining a matrixmaterial and reinforcing fibers or reinforcing particles. In particular,in the fields of semiconductor manufacturing instruments, opticalinstruments, microfabrication instruments, and the like, a reduction inthe effects of the thermal expansion of parts has been demanded.Therefore, composite materials using various reinforcing fibers such ascarbon fibers have been proposed (see WO00/64668, for example).

The inventors of the invention have proposed a carbon fiber compositematerial in which carbon nanofibers are uniformly dispersed in anelastomer (see JP-A-2005-68386, for example). In such a carbon fibercomposite material, the dispersibility of the carbon nanofibers withstrong aggregating properties is improved by mixing the elastomer withthe carbon nanofibers.

However, technology of uniformly dispersing the carbon nanofibers in athermosetting resin has not yet been established.

SUMMARY

According to a first aspect of the invention, there is provided a methodof producing a thermosetting resin composition comprising:

(a) mixing carbon nanofibers into an elastomer including an unsaturatedbond or a group having affinity to the carbon nanofibers, and dispersingthe carbon nanofibers by applying a shear force to obtain a compositeelastomer; and

(b) mixing the composite elastomer and a thermosetting resin.

According to a second aspect of the invention, there is provided amethod of producing a thermosetting resin composition comprising:

(c) mixing a thermosetting resin and an elastomer including anunsaturated bond or a group having affinity to carbon nanofibers; and

(d) mixing carbon nanofibers into the mixture of the thermosetting resinand the elastomer, and dispersing the carbon nanofibers by applying ashear force.

According to a third aspect of the invention, there is provided athermosetting resin composition obtained by any of the above-describedmethods.

According to a fourth aspect of the invention, there is provided athermosetting resin composition comprising:

a matrix including a thermosetting resin and an elastomer; and

carbon nanofibers dispersed in the matrix,

the elastomer including an unsaturated bond or a group having affinityto the carbon nanofibers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a view schematically showing a method of mixing an elastomerand carbon nanofibers utilizing an open-roll method according to oneembodiment of the invention.

FIG. 2 is a schematic enlarged view showing part of a compositeelastomer according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

The invention may provide a thermosetting resin composition in whichcarbon nanofibers are dispersed, and a method of producing the same.

According to one embodiment of the invention, there is provided a methodof producing a thermosetting resin composition comprising:

(a) mixing carbon nanofibers into an elastomer including an unsaturatedbond or a group having affinity to the carbon nanofibers, and dispersingthe carbon nanofibers by applying a shear force to obtain a compositeelastomer; and

(b) mixing the composite elastomer and a thermosetting resin.

According to the method of producing a thermosetting resin compositionaccording to this embodiment, a thermosetting resin composition in whichthe carbon nanofibers are uniformly dispersed can be easily obtained bymixing the composite elastomer, in which the carbon nanofibers areuniformly dispersed, with the thermosetting resin.

According to one embodiment of the invention, there is provided a methodof producing a thermosetting resin composition comprising:

(c) mixing a thermosetting resin and an elastomer including anunsaturated bond or a group having affinity to carbon nanofibers; and

(d) mixing carbon nanofibers into the mixture of the thermosetting resinand the elastomer, and dispersing the carbon nanofibers by applying ashear force.

According to the method of producing a thermosetting resin compositionaccording to this embodiment, the thermosetting resin can be providedwith the elasticity of the elastomer by obtaining the mixture of thethermosetting resin and the elastomer, and a thermosetting resincomposition in which the carbon nanofibers are uniformly dispersed canbe easily obtained. In order to disperse the carbon nanofibers in thematrix, the matrix material must exhibit viscosity, elasticity, andpolarity. The thermosetting resin and the elastomer exhibit viscosity.The elastomer exhibits elasticity. With regard to the polarity, theelastomer includes an unsaturated bond or a group having affinity to thecarbon nanofibers. Therefore, the carbon nanofibers can be relativelyeasily dispersed in the thermosetting resin composition.

In this method of producing a thermosetting resin composition, thecarbon nanofibers may have an average diameter of 0.5 to 500 nm.

In this method of producing a thermosetting resin composition, a networkcomponent of the elastomer in an uncrosslinked form may have a spin-spinrelaxation time (T2 n) measured at 30° C. by a Hahn-echo method using apulsed nuclear magnetic resonance (NMR) technique of 100 to 3,000microseconds.

In this method of producing a thermosetting resin composition, thethermosetting resin may be an epoxy resin; and the elastomer may be anepoxidized elastomer.

According to this configuration, since the epoxidized elastomer and theepoxy resin include an epoxy group having particularly excellentaffinity to the carbon nanofibers, the carbon nanofibers can beuniformly dispersed in the thermosetting resin composition.

According to one embodiment of the invention, there is provided athermosetting resin composition comprising:

a matrix including a thermosetting resin and an elastomer; and

carbon nanofibers dispersed in the matrix,

the elastomer including an unsaturated bond or a group having affinityto the carbon nanofibers.

In the thermosetting resin composition according to this embodiment, thecarbon nanofibers are uniformly dispersed in the matrix.

In this thermosetting resin composition, content of the elastomer in apolymer component formed of the elastomer, the thermosetting resin, anda curing agent for the thermosetting resin in the thermosetting resincomposition may be 10 to 40 wt %.

This provides a rigid thermosetting resin composition in which thecarbon nanofibers are uniformly dispersed. If the content of theelastomer in the thermosetting resin composition is less than 10 wt %,the dispersion of the carbon nanofiber becomes insufficient. If thecontent of the elastomer exceeds 40 wt %, the rigidity of thethermosetting resin composition is decreased.

In this thermosetting resin composition, the thermosetting resin may bean epoxy resin; and

the elastomer may be an epoxidized elastomer.

The thermosetting resin composition may have a dynamic modulus ofelasticity (E′) at 30° C. of 20 to 30 GPa.

This provides a thermosetting resin composition with a high rigiditysimilar to that of a metal structural material. Moreover, use of theepoxy resin enables the thermosetting resin composition to be moldedinto a desired shape at a low temperature in a short time in comparisonwith a metal material, whereby cost of the production process can bereduced. Moreover, a reduction in weight can be achieved.

The thermosetting resin composition may have an elongation at break of4% or more.

This provides a flexible thermosetting resin composition with a highrigidity similar to that of a metal material.

The elastomer according to this embodiment may be a rubber elastomer ora thermoplastic elastomer. As the raw material elastomer, anuncrosslinked form is used when using a rubber elastomer.

Embodiments of the invention are described below in detail withreference to the drawings.

As examples of a method of producing a thermosetting resin compositionaccording to this embodiment, the following two methods can be given.

(1) A method of producing a thermosetting resin composition according tothis embodiment includes: (a) mixing carbon nanofibers into an elastomerincluding an unsaturated bond or a group having affinity to the carbonnanofibers, and dispersing the carbon nanofibers by applying a shearforce to obtain a composite elastomer; and (b) mixing the compositeelastomer and a thermosetting resin.

(2) Another method of producing a thermosetting resin compositionaccording to this embodiment includes: (c) mixing a thermosetting resinand an elastomer including an unsaturated bond or a group havingaffinity to carbon nanofibers; and (d) mixing carbon nanofibers into themixture of the thermosetting resin and the elastomer, and dispersing thecarbon nanofibers by applying a shear force.

A thermosetting resin composition according to this embodiment includesa matrix including a thermosetting resin and an elastomer, and carbonnanofibers dispersed in the matrix, the elastomer including anunsaturated bond or a group having affinity to the carbon nanofibers.

The thermosetting resin and the elastomer are described below.

As the thermosetting resin, a thermosetting resin which is generallyused and exhibits excellent mutual solubility with the selectedelastomer may be appropriately selected. As examples of thethermosetting resin, polycondensed or addition-condensed resins such asa phenol resin, an amino resin, an epoxy resin, a silicone resin, athermosetting polyimide resin, and a thermosetting polyurethane resin,addition-polymerized resins such as a thermosetting acrylic resin, avinyl ester resin, an unsaturated polyester resin, and a diallylphthalate resin, and the like can be given. These thermosetting resinsmay be used either individually or in combination of two or more. As acuring agent for the thermosetting resin, a known curing agent may beappropriately selected corresponding to the thermosetting resin selecteddepending on the application.

In order to mix the carbon nanofibers into the matrix material anddisperse the carbon nanofibers, the matrix material is required toexhibit polarity for ensuring adsorption on the carbon nanofibers,viscosity and flowability for entering the space between the aggregatedcarbon nanofibers, and elasticity for refining (disentangling) thecarbon nanofibers due to strong shear force to uniformly disperse thecarbon nanofibers. Therefore, it is preferable that the thermosettingresin include a polar group. It is preferable to use the elastomer as anelastic component in order to satisfy the above elasticity requirement.

As the thermosetting resin including a polar group, it is preferable touse an epoxy resin having an epoxy group having excellent affinity tothe carbon nanofibers. The epoxy resin is not particularly limitedinsofar as the epoxy resin is generally industrially used. As examplesof a typical epoxy resin, epoxy resins having two or more epoxy groupsin the molecule such as a bisphenol A type epoxy resin produced frombisphenol A, a bisphenol F type epoxy resin produced from bisphenol F,and a bisphenol S type epoxy resin produced from bisphenol S can begiven. As a curing agent for the epoxy resin, a curing agent generallyindustrially used may be appropriately selected. As examples of thecuring agent, an amine curing agent, an acid anhydride curing agent, andthe like can be given.

The thermosetting resin such as the epoxy resin is liquid at atemperature employed in the step of mixing the thermosetting resin andthe elastomer and does not exhibit elasticity, differing from theelastomer, although the thermosetting resin exhibits viscosity.Therefore, even if the carbon nanofibers are mixed into thethermosetting resin, the carbon nanofibers cannot be dispersed. Forexample, when using an epoxidized elastomer as the elastomer, since theepoxy resin exhibits excellent mutual solubility with the epoxidizedelastomer, the mixture can be made uniform over the entire mixture inthe mixing step. Therefore, the carbon nanofibers adsorbed through theepoxy group (polarity) can be dispersed by utilizing the elasticity ofthe elastomer.

As the elastomer, an elastomer which provides the thermosetting resinwith rubber elasticity and exhibits excellent mutual solubility with theselected thermosetting resin may be appropriately selected. Theelastomer has a molecular weight of preferably 5,000 to 5,000,000, andstill more preferably 20,000 to 3,000,000. If the molecular weight ofthe elastomer is within this range, since the elastomer molecules areentangled and linked, the elastomer exhibits excellent elasticity fordispersing the carbon nanofibers. Since the elastomer exhibitsviscosity, the elastomer easily enters the space between the aggregatedcarbon nanofibers. Moreover, since the elastomer exhibits elasticity,the carbon nanofibers can be separated. If the molecular weight of theelastomer is less than 5,000, since the elastomer molecules cannot beentangled sufficiently, the effect of dispersing the carbon nanofibersis reduced due to low elasticity, even if a shear force is applied inthe subsequent step. If the molecular weight of the elastomer is greaterthan 5,000,000, the elastomer becomes too hard so that processingbecomes difficult.

The network component of the elastomer in an uncrosslinked form has aspin-spin relaxation time (T2 n/30° C.), measured at 30° C. by aHahn-echo method using a pulsed nuclear magnetic resonance (NMR)technique, of preferably 100 to 3,000 microseconds, and still morepreferably 200 to 1,000 microseconds. If the elastomer has a spin-spinrelaxation time (T2 n/30° C.) within the above range, the elastomer isflexible and has a sufficiently high molecular mobility. That is, theelastomer exhibits appropriate elasticity for dispersing the carbonnanofibers. Moreover, since the elastomer exhibits viscosity, theelastomer can easily enter the space between the carbon nanofibers dueto high molecular mobility when mixing the elastomer and the carbonnanofibers. If the spin-spin relaxation time (T2 n/30° C.) is shorterthan 100 microseconds, the elastomer cannot have a sufficient molecularmobility. If the spin-spin relaxation time (T2 n/30° C.) is longer than3,000 microseconds, since the elastomer tends to flow as a liquid, itbecomes difficult to disperse the carbon nanofibers due to lowelasticity.

The network component of the elastomer in a crosslinked form preferablyhas a spin-spin relaxation time (T2 n) measured at 30° C. by theHahn-echo method using the pulsed NMR technique of 100 to 2,000microseconds. The reasons therefor are the same as those described forthe uncrosslinked form. Specifically, when crosslinking theuncrosslinked form satisfying the above conditions, the spin-spinrelaxation time (T2 n) of the resulting crosslinked form almost fallswithin the above range.

The spin-spin relaxation time obtained by the Hahn-echo method using thepulsed NMR technique is a measure which indicates the molecular mobilityof a substance. In more detail, when measuring the spin-spin relaxationtime of the elastomer by the Hahn-echo method using the pulsed NMRtechnique, a first component having a shorter first spin-spin relaxationtime (T2 n) and a second component having a longer second spin-spinrelaxation time (T2 nn) are detected. The first component corresponds tothe network component (backbone molecule) of the polymer, and the secondcomponent corresponds to the non-network component (branched componentsuch as terminal chain) of the polymer. The shorter the first spin-spinrelaxation time, the lower the molecular mobility and the harder theelastomer. The longer the first spin-spin relaxation time, the higherthe molecular mobility and the softer the elastomer.

As the measurement method in the pulsed NMR technique, a solid-echomethod, a Carr-Purcell-Meiboom-Gill (CPMG) method, or a 90-degree pulsemethod may be applied instead of the Hahn-echo method. Since theelastomer according to the invention has a medium spin-spin relaxationtime (T2), the Hahn-echo method is most suitable. In general, thesolid-echo method and the 90-degree pulse method are suitable formeasuring a short spin-spin relaxation time (T2), the Hahn-echo methodis suitable for measuring a medium spin-spin relaxation time (T2), andthe CPMG method is suitable for measuring a long spin-spin relaxationtime (T2).

At least one of the main chain, side chain, and terminal chain of theelastomer includes an unsaturated bond or a group having affinity to thecarbon nanofiber, particularly to a terminal radical of the carbonnanofiber, or the elastomer has properties of readily producing such aradical or group. The unsaturated bond or group may be at least oneunsaturated bond or group selected from a double bond, a triple bond,and functional groups such as alpha-hydrogen, a carbonyl group, acarboxyl group, a hydroxyl group, an amino group, a nitrile group, aketone group, an amide group, an epoxy group, an ester group, a vinylgroup, a halogen group, a urethane group, a biuret group, an allophanategroup, and a urea group. In particular, the epoxy group exhibitsexcellent affinity to the carbon nanofiber.

The carbon nanofiber generally has a structure in which the side surfaceis formed of a six-membered ring of carbon atoms and the end is closedby introduction of a five-membered ring. However, since the carbonnanofiber has a forced structure, a defect tends to occur, so that aradical or a functional group tends to be formed at the defect. In thisembodiment, since at least one of the main chain, side chain, andterminal chain of the elastomer includes an unsaturated bond or a grouphaving high affinity (reactivity or polarity) to the radical of thecarbon nanofiber, the elastomer and the carbon nanofiber can be bonded.This enables the carbon nanofibers to be easily dispersed by overcomingthe aggregating force of the carbon nanofibers. When mixing theelastomer and the carbon nanofibers, free radicals produced due tobreakage of the elastomer molecules attack the defects of the carbonnanofibers to produce free radicals on the surfaces of the carbonnanofibers.

As the elastomer, an elastomer such as natural rubber (NR), epoxidizednatural rubber (ENR), styrene-butadiene rubber (SBR), nitrile rubber(NBR), chloroprene rubber (CR), ethylene propylene rubber (EPR or EPDM),butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM),silicone rubber (Q), fluorine rubber (FKM), butadiene rubber (BR),epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO or CEO),urethane rubber (U), or polysulfide rubber (T); a thermoplasticelastomer such as an olefin-based elastomer (TPO), poly(vinylchloride)-based elastomer (TPVC), polyester-based elastomer (TPEE),polyurethane-based elastomer (TPU), polyamide-based elastomer (TPEA), orstyrene-based elastomer (SBS); or a mixture of these elastomers may beused. In particular, a highly polar elastomer which readily producesfree radicals during mixing of the elastomer, such as natural rubber(NR) or nitrile rubber (NBR), is preferable. An elastomer having a lowpolarity, such as ethylene propylene rubber (EPDM), may also be used inthe invention, since such an elastomer also produces free radicals bysetting the mixing temperature at a relatively high temperature (e.g. 50to 150° C. for EPDM).

As the elastomer, an epoxidized elastomer, which is an elastomerincluding an epoxy group, is particularly preferable. Since theepoxidized elastomer includes an epoxy group having excellent affinityto the terminal radical of the carbon nanofiber, the carbon nanofiberscan be uniformly dispersed in the elastomer. As the epoxidizedelastomer, an elastomer including an epoxy group in the polymer, such asepoxidized natural rubber, an epoxidized styrene thermoplastic elastomer(e.g. E-SBS), a terminal epoxy-modified styrene-butadiene rubber(E-SBR), or the like may be used. The epoxidation rate of the epoxidizedelastomer is preferably 0.01 to 10%, and particularly preferably 0.5 to3%. If the amount of epoxy groups is less than 0.01%, the effect ofimproving the dispersibility of the carbon nanofibers is small. If theamount of epoxy groups exceeds 10%, the elastomer becomes hard toexhibit poor processability.

The elastomer according to this embodiment may be a rubber elastomer ora thermoplastic elastomer. When using a rubber elastomer, anuncrosslinked elastomer is preferably used.

The carbon nanofibers are described below.

The carbon nanofibers preferably have an average diameter of 0.5 to 500nm. In order to increase the strength of the thermosetting resincomposition, the average diameter of the carbon nanofibers is still morepreferably 0.5 to 30 nm.

The aspect ratio of the carbon nanofibers is preferably 50 or more, andstill more preferably 100 to 20,000.

As examples of the carbon nanofiber, a carbon nanotube and the like canbe given. The carbon nanotube has a single-wall structure in which agraphene sheet of a hexagonal carbon layer is closed in the shape of acylinder, or a multiwall structure in which the cylindrical structuresare nested. Specifically, the carbon nanotube may be formed only ofeither the single-wall structure or the multi-layer structure, or mayhave the single-wall structure and the multiwall structure incombination. A carbon material having a partial carbon nanotubestructure may also be used. The carbon nanotube may also be called agraphite fibril nanotube.

A single-wall carbon nanotube or a multiwall carbon nanotube is producedto a desired size using an arc discharge method, laser ablation method,vapor-phase growth method, or the like.

In the arc discharge method, an arc is discharged between electrodematerials made of carbon rods in an argon or hydrogen atmosphere at apressure lower than atmospheric pressure to a small extent to obtain amultiwall carbon nanotube deposited on the cathode. When a catalyst suchas nickel/cobalt is mixed into the carbon rod and an arc is discharged,a single-wall carbon nanotube is obtained from soot adhering to theinner side surface of the processing vessel.

In the laser ablation method, a target carbon surface into which acatalyst such as nickel/cobalt is mixed is irradiated with strong pulselaser light from a YAG laser in a noble gas (e.g. argon) to melt andvaporize the carbon surface to obtain a single-wall carbon nanotube.

In the vapor-phase growth method, a carbon nanotube is synthesized bythermally decomposing a hydrocarbon such as benzene or toluene in avapor phase. As specific examples of the vapor-phase growth method, afloating catalyst method, zeolite-supported catalyst method, and thelike can be given.

The carbon nanofibers may be provided with improved adhesion to andwettability with the elastomer by subjecting the carbon nanofibers to asurface treatment such as an ion-injection treatment, sputter-etchingtreatment, or plasma treatment before mixing the carbon nanofibers intothe elastomer.

The method (1) of producing a thermosetting resin composition accordingto this embodiment is described below.

The step (a) of mixing the carbon nanofibers into the elastomer anddispersing the carbon nanofibers by applying a shear force to obtain acomposite elastomer is described below.

The step (a) may be carried out by using an open-roll method, aninternal mixing method, a multi-screw extrusion kneading method, or thelike.

In this embodiment, an example using a open-roll method with a rolldistance of 0.5 mm or less is described as the step (a).

FIG. 1 is a diagram schematically showing the open-roll method using tworolls. In FIG. 1, a reference numeral 10 indicates a first roll, and areference numeral 20 indicates a second roll. The first roll 10 and thesecond roll 20 are disposed at a predetermined distance d (e.g. 1.5 mm).The first and second rolls are rotated normally or reversely. In theexample shown in FIG. 1, the first roll 10 and the second roll 20 arerotated in the directions indicated by the arrows.

When causing an elastomer 30 to be wound around the second roll 20 whilerotating the first and second rolls 10 and 20, a bank 32 of theelastomer 30 is formed between the rolls 10 and 20. After the additionof carbon nanofibers 40 to the bank 32, the first and second rolls 10and 20 are rotated to obtain a mixture of the elastomer and the carbonnanofibers. The mixture is then removed from the open rolls. Aftersetting the distance d between the first roll 10 and the second roll 20at preferably 0.5 mm or less, and still more preferably 0.1 to 0.5 mm,the mixture of the elastomer and the carbon nanofibers is supplied tothe open rolls and tight-milled to obtain a composite elastomer. Tightmilling is preferably performed about ten times, for example. When thesurface velocity of the first roll 10 is indicated by V1 and the surfacevelocity of the second roll 20 is indicated by V2, the surface velocityratio (V1/V2) of the first roll 10 to the second roll 20 during tightmilling is preferably 1.05 to 3.00, and still more preferably 1.05 to1.2. A desired shear force can be obtained by using such a surfacevelocity ratio.

This causes a high shear force to be applied to the elastomer 30 so thatthe aggregated carbon nanofibers 40 are separated in such a manner thatthe carbon nanofibers 40 are removed by the elastomer molecules one byone and are dispersed in the elastomer 30.

In this step, the elastomer and the carbon nanofibers are mixed at arelatively low temperature of preferably 0 to 50° C., and still morepreferably 5 to 30° C. in order to obtain as high a shear force aspossible. When using EPDM as the elastomer, it is preferable to performtwo-stage mixing steps. In the first mixing step, EPDM and the carbonnanofibers are mixed at a first temperature which is 50 to 100° C. lowerthan the temperature in the second mixing step in order to obtain ashigh a shear force as possible. The first temperature is preferably 0 to50° C., and still more preferably 5 to 30° C. A second temperature ofthe rolls is set at a relatively high temperature of 50 to 150° C. sothat the dispersibility of the carbon nanofibers can be improved.

In this step, free radicals are produced in the elastomer shorn by theshear force and attack the surfaces of the carbon nanofibers, wherebythe surfaces of the carbon nanofibers are activated. When using naturalrubber (NR) as the elastomer, the natural rubber (NR) molecule is cutwhile being mixed by the rolls to have a molecular weight lower than themolecular weight before being supplied to the open rolls. Radicals areproduced in the cut natural rubber (NR) molecules and attack thesurfaces of the carbon nanofibers during mixing, whereby the surfaces ofthe carbon nanofibers are activated.

Since the elastomer according to this embodiment has the above-describedcharacteristics, specifically, the above-described molecularconfiguration (molecular length), molecular motion, and chemicalinteraction with the carbon nanofibers, dispersion of the carbonnanofibers is facilitated. Therefore, a composite elastomer exhibitingexcellent dispersibility and dispersion stability (dispersed carbonnanofibers rarely reaggregate) of the carbon nanofibers can be obtained.In more detail, when mixing the elastomer and the carbon nanofibers, theelastomer having an appropriately long molecular length and a highmolecular mobility enters the space between the carbon nanofibers, and aspecific portion of the elastomer bonds to a highly active site of thecarbon nanofiber through chemical interaction. When a high shear forceis applied to the mixture of the elastomer and the carbon nanofibers inthis state, the carbon nanofibers move accompanying the movement of theelastomer, whereby the aggregated carbon nanofibers are separated anddispersed in the elastomer. The dispersed carbon nanofibers areprevented from reaggregating due to chemical interaction with theelastomer, whereby excellent dispersion stability can be obtained.

In the step (a), the above-mentioned internal mixing method ormulti-screw extrusion kneading method may be used instead of theopen-roll method. In other words, it suffices that this step apply ashear force to the elastomer sufficient to separate the aggregatedcarbon nanofibers and produce radicals by cutting the elastomermolecules.

In the step (a) of dispersing the carbon nanofibers in the elastomer, orin the subsequent step, a compounding ingredient usually used in theprocessing of an elastomer such as rubber may be added. As thecompounding ingredient, a known compounding ingredient may be used. Itis preferable that the composite elastomer be uncrosslinked. Acrosslinking agent may be mixed into the composite elastomer andcrosslinked in the step (b) in order to improve collapse resistance andcreep properties depending on the product application, for example.

The composite elastomer obtained by the step (a) is described below.

FIG. 2 is a schematic enlarged view showing part of the compositeelastomer according to this embodiment. In a composite elastomer 50, thecarbon nanofibers 40 are uniformly dispersed in the elastomer 30 as thematrix. In other words, the elastomer 30 is restrained by the carbonnanofibers 40. In this state, the mobility of the elastomer moleculesrestrained by the carbon nanofibers is low in comparison with the casewhere the elastomer molecules are not restrained by the carbonnanofibers.

The composite elastomer according to this embodiment preferably includesthe elastomer and 15 to 50 vol % of the carbon nanofibers dispersed inthe elastomer. If the amount of carbon nanofibers in the compositeelastomer is less than 15 vol %, the amount of carbon nanofibers in thethermosetting resin composition is decreased, whereby a sufficienteffect may not be obtained. If the amount of carbon nanofibers in thecomposite elastomer exceeds 50 vol %, processing in the step (a) becomesdifficult.

The composite elastomer mat include or may not include a crosslinkingagent depending on the application. When the composite elastomer doesnot include a crosslinking agent, since the matrix is not crosslinkedwhen forming the thermosetting resin composition, the matrix can berecycled.

In the composite elastomer according to this embodiment, the carbonnanofibers are uniformly dispersed in the elastomer as the matrix. Inother words, the elastomer is restrained by the carbon nanofibers. Inthis state, the mobility of the elastomer molecules restrained by thecarbon nanofibers is low in comparison with the case where the elastomermolecules are not restrained by the carbon nanofibers. Therefore, thefirst spin-spin relaxation time (T2 n), the second spin-spin relaxationtime (T2 nn), and the spin-lattice relaxation time (T1) of the compositeelastomer according to this embodiment are shorter than those of theelastomer which does not include the carbon nanofibers.

In a state in which the elastomer molecules are restrained by the carbonnanofibers, the number of non-network components (non-reticulate chaincomponents) is considered to be reduced for the following reasons.Specifically, when the molecular mobility of the elastomer is entirelydecreased by the carbon nanofibers, since the number of non-networkcomponents which cannot easily move is increased, the non-networkcomponents tend to behave in the same manner as the network components.Moreover, since the non-network components (terminal chains) easilymove, the non-network components tend to be adsorbed on the active sitesof the carbon nanofibers. It is considered that these phenomena decreasethe number of non-network components. Therefore, the fraction (fnn) ofcomponents having the second spin-spin relaxation time is smaller thanthat of the elastomer which does not include the carbon nanofibers.

Therefore, the composite elastomer according to this embodimentpreferably has values measured by the Hahn-echo method using the pulsedNMR technique within the following range.

Specifically, it is preferable that, in the uncrosslinked compositeelastomer, the first spin-spin relaxation time (T2 n) measured at 150°C. be 100 to 3,000 microseconds, the second spin-spin relaxation time(T2 nn) measured at 150° C. be 1,000 to 10,000 microseconds, and thefraction (fnn) of components having the second spin-spin relaxation timebe less than 0.2.

It is preferable that, in the crosslinked composite elastomer, the firstspin-spin relaxation time (T2 n) measured at 150° C. be 100 to 2,000microseconds, the second spin-spin relaxation time (T2 nn) measured at150° C. be absent or 1,000 to 5,000 microseconds, and the fraction (fnn)of components having the second spin-spin relaxation time be less than0.2.

The spin-lattice relaxation time (T1) measured by the inversion recoverymethod using the pulsed NMR technique is a measure indicating themolecular mobility of a substance together with the spin-spin relaxationtime (T2). In more detail, the shorter the spin-lattice relaxation timeof the elastomer, the lower the molecular mobility and the harder theelastomer. The longer the spin-lattice relaxation time of the elastomer,the higher the molecular mobility and the softer the elastomer.Therefore, the composite elastomer in which the carbon nanofibers areuniformly dispersed exhibits low molecular mobility which falls withinthe above T2 n, T2 nn, and fnn ranges.

The composite elastomer according to this embodiment preferably has aflow temperature, determined by temperature dependence measurement ofdynamic viscoelasticity, 20° C. or more higher than the flow temperatureof the raw material elastomer. In the composite elastomer according tothis embodiment, the carbon nanofibers are uniformly dispersed in theelastomer. In other words, the elastomer is restrained by the carbonnanofibers, as described above. In this state, the elastomer exhibitsmolecular motion smaller than that of an elastomer which does notinclude the carbon nanofibers, whereby flowability is decreased.

The step (b) of mixing the composite elastomer and the thermosettingresin is described below.

The step (b) may be carried out by using the open-roll method, theinternal mixing method, the multi-screw extrusion kneading method, orthe like in the same manner as the step (b). For example, when carryingout the step (b) by the multi-screw extrusion kneading method using atwin-screw extruder, the thermosetting resin and the composite elastomerare supplied to the twin-screw extruder, and melted and mixed. Thecomposite elastomer is dispersed in the thermosetting resin by rotatingthe screws of the twin-screw extruder. The thermosetting resincomposition is extruded from the twin-screw extruder. The extrudedthermosetting resin composition may be cured by heating underpredetermined heating conditions of the thermosetting resin used. Acrosslinking agent may be added to the twin-screw extruder in the step(b), or a crosslinking agent may be added in advance in the step (a),and the composite elastomer may be crosslinked. For example, the curedthermosetting resin composition may be crosslinked by heating thethermosetting resin composition at a crosslinking temperature.

As the elastomer used in the step (a), an appropriate elastomer whichexhibits excellent mutual solubility with the thermosetting resin usedin the step (b) is preferably selected. For when the thermosetting resinis an epoxy resin, the elastomer is preferably an epoxidized elastomersuch as epoxidized styrene-butadiene rubber (E-SBS). When thethermosetting resin is a phenol resin, the elastomer is preferably NBRor E-SBS.

The amount of the composite elastomer in the thermosetting resincomposition is preferably 2 vol % to 50 vol %. The amount of the Carbonnanofibers in the thermosetting resin composition is preferably 0.3 vol% to 25 vol %. If the amount of the composite elastomer in thethermosetting resin composition is less than 2 vol %, the amount ofcarbon nanofibers in the thermosetting resin composition is decreased,whereby a sufficient effect may not be obtained. If the amount of thecomposite elastomer in the thermosetting resin composition exceeds 50vol %, the processing in the step (b) becomes difficult.

The method (2) of producing a thermosetting resin composition accordingto this embodiment is described below.

The step (c) of mixing the thermosetting resin and the elastomer and thestep (d) of mixing the carbon nanofibers into the mixture of thethermosetting resin and the elastomer, and dispersing the carbonnanofibers by applying a shear force are described below.

The step (c) may be carried out using the open-roll method using a resinroll, the internal mixing method, the multi-screw extrusion kneadingmethod, or the like. Since the liquid thermosetting resin (base resin)is mixed with the elastomer, a mixer (processing machine) is selecteddepending on the viscosity. When using the liquid thermosetting resin asin this embodiment, an internal mixer such as a Henschel mixer ispreferable. An open roll using three rolls or two rolls may also beused. For example, when carrying out the step (c) by the multi-screwextrusion kneading method using a twin-screw extruder, the thermosettingresin and the elastomer are supplied to the twin-screw extruder, andmelted and mixed. The elastomer is dispersed in the thermosetting resinby rotating the screws of the twin-screw extruder. When carrying out thestep (c) using an open roll with two rolls, the rolls are rotated at aroll distance of preferably 0.5 to 5 mm (e.g. 1.0 mm) to caused theelastomer to be wound around one of the rolls. After the addition of thethermosetting resin to the bank, the elastomer and the thermosettingresin are mixed. When carrying out the mixing step (c) at a lowtemperature, a curing agent may be added in the step (c). In this case,the rotational speed of one of the rolls is 20 rpm, and the rotationalspeed of the other roll is 22 rpm, for example. This caused theelastomer and the thermosetting resin to be mixed to obtain asheet-shaped mixture.

In the step (d), the carbon nanofibers are supplied to and mixed intothe mixture of the thermosetting resin and the elastomer provided in thetwin-screw extruder in a molten state. A high shear force is applied tothe mixture by rotating the screws, whereby the aggregated carbonnanofibers are separated so that the carbon nanofibers are pulled one byone by the elastomer molecules in the mixture, and dispersed in themixture. The thermosetting resin composition is then extruded from thetwin-screw extruder. The extruded thermosetting resin composition may becured by heating under predetermined heating conditions of thethermosetting resin used. A crosslinking agent may be added to thetwin-screw extruder in the step (c) or (d), and the composite elastomermay be crosslinked. For example, the cured thermosetting resincomposition may be crosslinked by heating the thermosetting resincomposition at a crosslinking temperature. For example, when carryingout the step (d) using an open roll after the step (c), After theaddition of the carbon nanofibers to the bank of the mixture, themixture and the carbon nanofibers are mixed by rotating the two rolls,and the mixture is tight-milled a number of times. In this case, therotational speed of the roll is the same as in the step (c). Afterreducing the roll distance to preferably 0.1 mm to 0.5 mm (e.g. 0.1 mm),the rolls are rotated (the roll surface rotational speed ratio is 1.1,for example). This causes a high shear force to be applied to themixture discharged from the rolls. The shear force causes the aggregatedcarbon nanofibers to be separated so that the carbon nanofibers arepulled one by one and to be dispersed in the mixture. After increasingthe roll surface rotational speed ratio 1.3 (e.g. 26 rpm/20 rpm), themixture is rolled at a roll distance of 0.5 mm, for example, to obtain asheet-shaped thermosetting resin composition.

In the step of curing the thermosetting resin composition, a generalthermosetting resin molding method may be employed. For example, thethermosetting resin composition including a curing agent may be placedin a mold heated at a specific temperature, and compression-molded at aspecific pressure. Or, the thermosetting resin composition may be moldedusing a transfer molding machine or the like. The molding temperatureand the molding time may be appropriately set depending on the types ofselected thermosetting resin and curing agent. In the thermosettingresin composition pressurized in the heated mold for a specific periodof time, the epoxy resin is crosslinked and cured due to the presence ofthe curing agent. The thermosetting resin composition is then removedfrom the mold.

As the elastomer used in the steps (c) and (d), an appropriate elastomerwhich exhibits excellent mutual solubility with the thermosetting resinis preferably selected in the same manner as in the steps (a) and (b).For when the thermosetting resin is an epoxy resin, the elastomer ispreferably an epoxidized elastomer such as epoxidized styrene-butadienerubber (E-SBS). When the thermosetting resin is a phenol resin, theelastomer is preferably NBR or E-SBS.

The elastomer content in the polymer component (i.e. the elastomer, thethermosetting resin, and the curing agent for the thermosetting resin)in the thermosetting resin composition is preferably 10 to 40 wt %. Thisprovides a rigid thermosetting resin composition in which the carbonnanofibers are uniformly dispersed. If the elastomer content in thepolymer component is less than 10 wt %, the dispersion of the carbonnanofiber becomes insufficient. If the elastomer content exceeds 40 wt%, the rigidity of the thermosetting resin composition is decreased.

The carbon nanofiber content in the thermosetting resin compositionpreferably 0.3 to 45 wt %, and still more preferably 8 to 30 wt %. Ifthe carbon nanofiber content is less than 0.3 wt %, the rigid of thethermosetting resin composition is not sufficiently increased. If thecarbon nanofiber content exceeds 45 wt %, processing becomes difficultto too high a rigidity.

The thermosetting resin composition is described below.

The thermosetting resin composition according to this embodimentincludes the matrix including the thermosetting resin and the elastomer,and the carbon nanofibers dispersed in the matrix, the elastomerincluding an unsaturated bond or a group having affinity to the carbonnanofibers.

The thermosetting resin composition exhibits improved strength,rigidity, durability, and the like in comparison with the thermosettingresin, since the carbon nanofibers are uniformly dispersed in thematrix. The thermosetting resin composition exhibits improved impactresistance due to incorporation of the elastomer component. Inparticular, a thermosetting resin composition in which the thermosettingresin is an epoxy resin and the elastomer is an epoxidized elastomerpreferably has a high rigidity with a dynamic modulus of elasticity (E′)at 30° C. of 20 to 30 GPa and an elongation at break of 4% or more.

EXAMPLES

Examples according to the invention and comparative examples aredescribed below. Note that the invention is not limited to the followingexamples. (Examples 1 to 7 and Comparative Examples 1 to 3)

(1) Preparation of Sample

Step (c)

An epoxidized elastomer was supplied to a 6-inch open roll (rolltemperature: 10 to 50° C.) and wound around the roll. An epoxy resin(base resin) was supplied to and mixed with the epoxidized elastomer toobtain a first mixture. The roll distance was set at 1 mm, and the rollrotational speed was set at 22 rpm/20 rpm. The types and amounts (phr)of the epoxidized elastomer and the epoxy resin are shown in Tables 1and 2.

Step (d)

A filler was supplied to and mixed with the first mixture. Afterreducing the roll distance to 0.1 mm, the mixture was tight-milled fivetimes to obtain a second mixture. The roll rotational speed was set at22 rpm/20 rpm. After setting the roll distance at 1 mm and the rollrotational speed at 22 rpm/20 rpm, the second mixture was supplied tothe open roll. A curing agent was then supplied to and mixed with thesecond mixture. The type and amount (phr) of the filler are shown inTables 1 and 2. The roll temperature was set at 10° C. to 50° C.

The second mixture including the curing agent was removed from the openroll and placed in a mold with a thickness of 2 mm. The second mixturewas press-molded at 150° C. for five minutes at a pressure of 10 MPa toobtain a cured (crosslinked) thermosetting resin composition sample.

In Tables 1 and 2, the base resin “Epikote 828” of the epoxy resin is abisphenol A type epoxy resin manufactured by Japan Epoxy Resins Co.,Ltd. (viscosity: 120 to 150 poise/25° C., epoxy equivalent: 172 to 178).In Tables 1 and 2, the curing agent “Amicure VDH” for the epoxy resin isa hydrazide curing agent manufactured by Ajinomoto fine Techno Co., Inc.(white powder, melting point: 120° C.). In Tables 1 and 2, theepoxidized elastomer “E-SBS” is an epoxidized styrene-butadiene blockcopolymer manufactured by Daicel Chemical Industries, Ltd. (EpofriendA1005 (molecular weight 100,000, epoxidation rate: 1.7%)). In Tables 1and 2, “CNT3” is a multi-wall carbon nanotube (CVD) with an averagediameter of 13 nm (manufactured by ILJIN Nanotech Co., Ltd.), and “HAF”is HAF grade carbon black with an average diameter of 27 nm.

In Tables 1 and 2, the “elastomer content (wt %)” is the content of theepoxidized elastomer in the polymer component (base resin+curingagent+epoxidized elastomer), and the “filler content (wt %)” is thecontent of the filler in the thermosetting resin composition (epoxyresin+epoxidized elastomer+filler).

(2) Measurement of Tensile Strength (MPa)

A specimen prepared by cutting each sample in the shape of a 1A dumbbellwas subjected to a tensile test in accordance with JIS K7161 at atemperature of 23±2° C. and a tensile rate of 500 mm/min using a tensiletester manufactured by Toyo Seiki Seisaku-sho, Ltd. to measure thetensile strength (MPa). The results are shown in Tables 1 and 2.

(3) Measurement of Elongation at Break (%)

A specimen prepared by cutting each sample in the shape of a dumbbell inaccordance with JIS-K6251-1993 was subjected to a tensile fracture testat a temperature of 23±2° C. and a tensile rate of 500 mm/min using atensile tester manufactured by Toyo Seiki Seisaku-sho, Ltd. to measurethe elongation at break (%). The results are shown in Tables 1 and 2.

(4) Measurement of Dynamic Modulus of Elasticity (GPa)

A specimen prepared by cutting each sample in the shape of a strip(40×1×5 (width) mm) was subjected to a dynamic viscoelasticity test at achuck distance of 20 mm, a temperature of 30° C., a dynamic strain of±0.05, and a frequency of 10 Hz using a dynamic viscoelasticity testingmachine DMS6100 manufactured by SII to measure the dynamic modulus ofelasticity (E′) at 30° C. The results are shown in Tables 1 and 2.

(5) Measurement Using Pulsed NMR Technique

Each epoxidized elastomer was subjected to measurement by the Hahn-echomethod using the pulsed NMR technique. The measurement was conductedusing “JMN-MU25” manufactured by JEOL, Ltd. The measurement wasconducted under conditions of an observing nucleus of ¹H, a resonancefrequency of 25 MHz, and a 90-degree pulse width of 2 microseconds, anda decay curve was determined while changing Pi in the pulse sequence(90°x-Pi-180°x) of the Hahn-echo method. The sample was measured in astate in which the sample was inserted into a sample tube within anappropriate magnetic field range. The measurement temperature was 30° C.The first component (T2 n) of the spin-spin relaxation time of theepoxidized elastomer was measured by this measurement. The spin-spinrelaxation time (T2 n) of the epoxidized elastomer “E-SBS” was 860(microsecond). TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Example 7 Epoxy Base resin Epikote 828 (phr) 100 100 100 100100 100 100 resin Curing agent Amicure VDH (phr) 40 40 40 40 40 40 40Epoxidized elastomer E-SBS (phr) 50 50 20 80 50 50 100 T2n of elastomer(30° C.) (microsecond) 860 860 860 860 860 860 860 Elastomer content (wt%) 26.3 26.3 12.5 36.4 26.3 26.3 41.7 Filler CNT CNT13 (phr) 40 20 20 2080 100 20 CB HAF (phr) 0 0 0 0 0 0 0 Filler content (wt %) 17.4 9.5 11.18.3 29.6 34.5 7.7 Properties of Tensile strength (MPa) 33 41 37 48 48 3028 thermosetting Elongation at break (%) 6 8 7 16 4 2 25 resincomposition Modulus of elasticity 21 25 29 20 29 22 18 E′(30° C.) (GPa)

TABLE 2 Comparative Comparative Comparative Example 1 Example 2 Example3 Epoxy Base resin Epikote 828 (phr) 100 100 100 resin Curing agentAmicure VDH (phr) 40 40 40 Epoxidized elastomer E-SBS (phr) 0 50 50 T2nof elastomer (30° C.) (microsecond) 0 860 860 Elastomer content (wt %)0.0 26.3 26.3 Filler CNT CNT13 (phr) 0 0 0 CB HAF (phr) 0 0 50 Fillercontent (wt %) 0.0 0.0 20.8 Properties of Tensile strength (MPa) 30 1513 thermosetting Elongation at break (%) 2 8 6 resin composition Modulusof elasticity E′(30° C.) (GPa) 18 3.8 19

As shown in Tables 1 and 2, the dynamic modulus of elasticity inExamples 1 to 7 using the multi-wall carbon nanotube (CNT13) was higherthan those of Comparative Examples 1 and 2 in which a filler was notused and Comparative Example 3 using another filler (carbon black). Thedynamic modulus of elasticity was 20 GPa or more even in Example 4 inwhich the carbon nanofiber content was 8.3 wt %. Moreover, thethermosetting resin compositions of Examples 1 to 7 exhibitedflexibility due to incorporation of a moderate amount of the epoxidizedelastomer. In particular, the thermosetting resin compositions ofExamples 1 to 5 and 7 exhibited an elongation at break of 4% or more. InExample 6 with a carbon nanofiber content of 34.5 wt %, the elongationat break was as small as 2%. In Example 7 with a carbon nanofibercontent of less than 8 wt %, the dynamic modulus of elasticity was lessthan 20 GPa.

From the above results, it was confirmed that the thermosetting resincomposition according to the invention exhibits high rigidity and highflexibility.

Although only some embodiments of the invention have been described indetail above, those skilled in the art will readily appreciate that manymodifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of the invention.

1. A method of producing a thermosetting resin composition comprising:(a) mixing carbon nanofibers into an elastomer including an unsaturatedbond or a group having affinity to the carbon nanofibers, and dispersingthe carbon nanofibers by applying a shear force to obtain a compositeelastomer; and (b) mixing the composite elastomer and a thermosettingresin.
 2. The method of producing a thermosetting resin composition asdefined in claim 1, wherein the carbon nanofibers have an averagediameter of 0.5 to 500 nm.
 3. The method of producing a thermosettingresin composition as defined in claim 1, wherein a network component ofthe elastomer in an uncrosslinked form has a spin-spin relaxation time(T2 n) measured at 30° C. by a Hahn-echo method using a pulsed nuclearmagnetic resonance (NMR) technique of 100 to 3,000 microseconds.
 4. Themethod of producing a thermosetting resin composition as defined inclaim 1, wherein the thermosetting resin is an epoxy resin; and whereinthe elastomer is an epoxidized elastomer.
 5. A thermosetting resincomposition obtained by the method as defined in claim
 1. 6. A method ofproducing a thermosetting resin composition comprising: (c) mixing athermosetting resin and an elastomer including an unsaturated bond or agroup having affinity to carbon nanofibers; and (d) mixing carbonnanofibers into the mixture of the thermosetting resin and theelastomer, and dispersing the carbon nanofibers by applying a shearforce.
 7. The method of producing a thermosetting resin composition asdefined in claim 6, wherein the carbon nanofibers have an averagediameter of 0.5 to 500 nm.
 8. The method of producing a thermosettingresin composition as defined in claim 6, wherein a network component ofthe elastomer in an uncrosslinked form has a spin-spin relaxation time(T2 n) measured at 30° C. by a Hahn-echo method using a pulsed nuclearmagnetic resonance (NMR) technique of 100 to 3,000 microseconds.
 9. Themethod of producing a thermosetting resin composition as defined inclaim 6, wherein the thermosetting resin is an epoxy resin; and whereinthe elastomer is an epoxidized elastomer.
 10. A thermosetting resincomposition obtained by the method as defined in claim
 6. 11. Athermosetting resin composition comprising: a matrix including athermosetting resin and an elastomer; and carbon nanofibers dispersed inthe matrix, the elastomer including an unsaturated bond or a grouphaving affinity to the carbon nanofibers.
 12. The thermosetting resincomposition as defined in claim 11, wherein content of the elastomer ina polymer component formed of the elastomer, the thermosetting resin,and a curing agent for the thermosetting resin in the thermosettingresin composition is 10 to 40 wt %.
 13. The thermosetting resincomposition as defined in claim 11, wherein the thermosetting resin isan epoxy resin; and wherein the elastomer is an epoxidized elastomer.14. The thermosetting resin composition as defined in claim 13, having adynamic modulus of elasticity (E′) at 30° C. of 20 to 30 GPa.
 15. Thethermosetting resin composition as defined in claim 14, having anelongation at break of 4% or more.